Process of purifying aluminous materials.



V materials such v the alloys of these metals,

in the molten bath of alumina and incapable of a Suifi nt prop UNITEDSTATES PATE LEWIS E. sAunnnns, or NIAGARA FALLS, new YORK, ASSIGNOR To noa'ron ooMrANY, or woncnsrnn, mAssAenusnrrs, A conroRArIon or MASSACHUSETTS.

Specification of Letters Patent.

Patented June "3, i910.

No Drawing. Application filed fieptember 14, 19(19. Serial No. 517,706.

To all whom it may concern:

SAUNDERS, States, residing at The object of this invention is the provision of a process of purifying aluminous as bauxite, clay, etc., and producing therefrom a commercially pure alumina, which is well adapted to the various uses to which such material may heapplied, as for example as an abrasive'or refractory. material, as a source of aluminum, etc.

The process is particularly advantageous as applied to aluminous materials which are relatively high in silica, as for example silicious bauxites and clays.

' It has been proposed heretofore to purify bauxite by the addition to the calcined material of a certain proportion of carbon, usually about 10 per cent, and the fusion of the mixture in an electric furnace, the carbon being proportioned to the quantity of reducible impurities in the bauxite and combining with a portion of these with formation of an alloy which segregates from the molten mass. In practice however it has not been possible to secure by this method a complete or substantially complete elimination of the impurities, especially titanium. If the amount of carbon used becarefully proportioned to the percentage of reducible impurities, it will be found that the reduction is quite incomplete; and if-carbon be used in some excess of this proportion it is found that the reduction is still incomplete, and furthermore that the product is contaminated by the presence of carbid of aluminum and compounds of the associated metals. It appears as a probable explanation of this phenomenon that whereas the metals iron, silicon and titanium, which are commonly associated with aluminum, and are quite insoluble of difl'using therethrough, their carbids are more or less readily soluble in or miscible wi h h h, th r ul ing hat t u carhids or carburlzed compounds of the associated metals results in their being again taken up by the molten bath, or in their failortion of carbon to form.

ure to separate therefrom. It is not however to be inferred, that the metals are necessarily redissolved or difi'used through the bath as carbids, for it is quite probable that the carbon may serve as a carrier of oxygen between the alumina and the reduced impurities, whereby these are returned to the molten bath as oxids or oxidized compounds.

According to the present invention I make use of the strong reducing properties of aluminum carbid to securea more nearly" complete elimination of the metals or 1m purities associated with the alumina than has heretofore been practicable: and in the embodiment of the invention wherein it is applied to the treatment of clays or of bauxites high in silica, I further make use of theknown fact that silicon is capable of preventing the absorption of large proportions of carbon by such metals as iron and titanium. In the preferred embodiment of the invention I add to silicious bauxite or clay a proportion of carbon largely in excess of that required to reduce the iron, silicon and titanium therein, and fuse the mass in a suitable electric furnace, whereby a considerable portion or even all of the alumina is converted into aluminum carbid. This carbid is capable of mixing with molten alumina or of dissolving or diffusing therein, and when so dissolved or diifused, or when in a molten condition, is a most energetic reducing agent, by the action of which, supplementing that of the carbon, the oxids of the assoclated impurities are reduced with substantial completeness: at the same time the reduced metal or alloy is by its content of silicon prevented from absorbingJ or combining with such proportion of car on as would bring about an amount of re-solution or difi'uslon capable of contaminating the bath to a de ee rendering it unfit or objectionable for lndustrial, urposes. Thereafter the aluminum carbi or the mixture of alumina and aluminum carbid, is separated from the reduced impurities and is oxidized, preferably while yet in a molten condition, with the result that a homogeneous mass of commercially pure alumina is obtained.

In the practice of the invention, I mix calcined silicious bauxite or clay. with an amount of carbon very considerably in excess of that theoretically required to reduce the associated oxids of iron, silicon and ticomplete conversion of the alumina into carbid is unnecessary and to a certain extent wasteful, but it is essential that enough aluminum carbid should be formed to bring about with the desired completeness the reduction of the oxidized compounds associated with the alumina. V

The reduced metals are allowed to settle from the molten bath of aluminum carbid, or alumina and aluminum carbid, and are removed therefrom, preferably by tapping either the reduced metals or the molten bath.

The molten bath, substantially free from metals other than aluminum, is then oxidized in any suitable way, as for example by blowing an oxidizing gas, usually air, through the molten mass in the furnace or after tapping, in a trough or other recepta-' cle, by showering the molten mass through the air, by spattering orotherwise subdividing it' in air, etc. This reaction is strongly exothermic, and the fluidity of the bath is increased by the heat set free, whereby the operation of blowing and any pouring or tap; ping operation is rendered easier than would otherwise be the case. Obviously the temperature may be maintained if necessary during either or both of these operations by a supply of heat from other sources. The fully oxidized mass, free or substantially free from aluminum carbid and consisting essentially of previously molten alumina, may be permitted to solidify in place, poured or tapped, or otherwise treated as desired.

I claim:

1. The process of purifying aluminous materials which consists in fusing the same in .presence of carbon in excess of that required to reduce the associated impurities, thereby reducing the associated impurities and producing a molten bathcontainin aluminum carbid, separating the reduce impurities, and then oxidizing the aluminum carbid by means of an oxidizing gas.

2. The process of purifying aluminous materials which consists in fusing the same in presence of carbon in excess of that reuired to reduce the associated impurities, t ereby reducing the associated impurities and producin a molten bath containing aluminum car id, separating the reduced impurities, and oxidizing the aluminum carbid while in a molten state.

3. The process of purifying aluminous materials which consists in fusing the same in presence of carbon in excess of that required to reduce the associated impurities, thereby reducing the associated impurities and producing a molten bath containing aluminum carbid, separating the reduced impurities, and oxidizing the aluminum carbid by exposing the same in amolten state to the action of an oxidizin gas.

4. The process of purifymg aluminous materials which consists in fusing the same in presence of carbon in excess of that required to reduce the associated impurities, thereby reducing the associated impurities and producing a molten bath containing aluminum carbid, separating the reduced impurities, and oxidizing the aluminum carbid by blowing an oxidizing gas through the molten bath.

5. The process of purifying aluminous materials containing silicon and metals ca-.

pable of alloying therewith which consists in using the same in presence of carbon in excess of that required to reduce the associated impurities, thereby reducing the associated impurities and producing an alloy high in silicon and low in carbon and a molten bath containing aluminum carbid, separating the alloy, and then oxidizing the aluminum carbid by means of an oxid zing 7 6. The process of purifying aluminous materials containin silicon and metals capable of alloying t erewith which consists in fusing the same 'inresence of carbon in excess of that require to reduce the associated impurities, thereby reducing the associated impurities and producin an alloy high in sllicon and low in car on and a molten bath containing aluminum carbid, separating the alloy, and oxidizing the aluminum carbid while in a molten state.

7. The process of urifying aluminous materials containin @con and metals capable of alloying t erewith which consists in fusing the same in resence of carbon in excess of that require to reduce the associated impurities, thereby reducing the associated im urities and produc' an alloy high in sllicon and low in car on and a molten bath containing aluminum carbid, separating the alloy, and oxidizing the aluminum carbid by exposing the same in a molten state to the action of an oxidizing 8. The process of gurifying aluminous materials containing s1 icon and metals capable of alloying therewith which conists 1n fusing the same in resence of carbon in ex-- cess of that require to reduce the assoc ated impurities, thereby reducing'the associated impurities and producing an alloy high 1n sillcon and low in carbon and a molten bath containing aluminum carbid, separatlng the alloy, and oxidizin the aluminum carbid by blowin an oxidizing gas through the molten bat 9. The process of purifying alu'minous materials which consists in reducing theimpurities by means of aluminum carbid in excess, separatlng the reduced lmpurltles, and then oxldlzmg the remaining alummum 'earbid by means of an oxidizing gas.

10. The process of purifying aluminous materials Which consists in reducing the impurities by means of aluminum carbid in ex- 10 cess, separating the reduced impurities, and

LEWIS E. SAUNDERS.

Witnessesz' SAMUEL F. HALL, NEIL A. l/VILsoN, 

